Factors destabilizing the control of Monochoria vaginalis by rice bran: its conflicting powers influence both suppression and promotion of germination in paddy soil

Abstract

Organic paddy rice (Oryza sativa L.) cultivation can be negatively impacted because of the weeds growth like Monochoria vaginalis. Although the rice bran application is useful in combating weed, its performance is not consistent. In this study, laboratory experiments were conducted to elucidate the effects of rice bran on the suppression and promotion of germination of M. vaginalis. Suppression experiments involved incubating mixtures of flooded soil and rice bran. This was followed by a germination experiment in the collected soil solutions. A negative and significant correlation was observed between germination and the electric conductivity (EC) of the solution. None of the seeds germinated when the EC of the Gray Lowland soil was over 130 mS m −1 . Conversely, the seeds in the Andosols' solution germinated even when EC was over 130 mS m −1 . Thus, the solutions of the Andosols had different mechanisms of suppression than the Gray Lowland soils. To understand the promotion of germination, air-dried soil was prepared after the flooded incubation of rice bran and soil mixture, simulating a long-term application of rice bran. Germination was analyzed in a filtrate of the mixture of air-dried soil and distilled water. The addition of rice bran significantly promoted germination. There was a negative and significant correlation between germination and dissolved oxygen (DO) suggesting that hardly decomposable components like antioxidants in rice bran decreased O 2 and stimulated germination because the seeds of M. vaginalis require very little O 2 for germination.

Suppressive activity of volatile fatty acids and aromatic carboxylic acids on the germination of Monochoria vaginalis

“…The suppression of M. vaginalis by rice bran application is associated with chemical factors indicated by electrical conductivity (EC) increase (Nozoe et al, 2021(Nozoe et al, , 2012, as well as physical ones, namely, the settled soil volume in water (Nozoe et al, 2016). We have shown that rice bran application increased the EC of soil solution, possibly because of the increased ionic compounds from rice bran decomposition, and M. vaginalis germination suppression is increased along with the EC value (Nozoe et al, 2021(Nozoe et al, , 2012. Organic acids are generally released during rice bran or organic matter decomposition in the paddy soil.…”

Effect of Gibberellic Acid and Germination Medium on Kiwifruit Seed Germination

“…The lowest value was observed in treatments with rice bran followed by compost. Low germination percentage in rice bran might be because of the presence of numerous antioxidant substances which cannot be decomposed easily (Nozoe et al, 2021). Whereas, compost performs better as a soil amendment.…”